Issue 5183 - Provide async interface for FileSystem

src/Thread.h

Index: src/Thread.h
===================================================================
--- a/src/Thread.h
+++ b/src/Thread.h
@@ -13,24 +13,70 @@
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #ifndef ADBLOCKPLUS_THREAD_H
 #define ADBLOCKPLUS_THREAD_H
 
+#include <chrono>
+#include <condition_variable>
+#include <mutex>
+#include <string>
+
 #ifdef WIN32
 #include <windows.h>
 #else
 #include <pthread.h>
 #endif
 
 namespace AdblockPlus
 {
+  class Sync
+  {
+  public:
+    Sync()
+      : set(false)
+    {
+    }
+    template<class R = typename std::chrono::seconds::rep,
+             class P = std::ratio<1>>
+    void Wait(const std::chrono::duration<R, P>& duration = std::chrono::seconds(20))
+    {
+      std::unique_lock<std::mutex> lock(mutex);
+      while (!set)
+      {
+        if (duration == std::chrono::duration<R>::zero())
+          cv.wait(lock);
+        else
+          cv.wait_for(lock, duration);
+      }
+    }

[sergei, 2017/07/03 09:25:56]

Zero seems even less appropriate here but OK, I think it should not be an issue
currently. BTW, what about returning of member `set` from `Wait`?

[hub, 2017/07/04 19:58:27]

I wasn't super thrilled about it either.
Maybe we can have a `WaitFor` that takes the duration and have `Wait` not
timeout.
`WaitFor` will return false if timeout occured.

[sergei, 2017/07/05 10:03:20]

I thought about it too, it actually looks very good.

+    void Set(const std::string& err = std::string())
+    {
+      {
+        std::unique_lock<std::mutex> lock(mutex);
+        set = true;
+        error = err;
+      }
+      cv.notify_all();
+    }
+    std::string GetError()
+    {
+      std::unique_lock<std::mutex> lock(mutex);
+      return error;
+    }
+  private:
+    std::mutex mutex;
+    std::condition_variable cv;
+    bool set;

[sergei, 2017/07/03 09:25:55]

would it be better to call it as `isSet`?

[hub, 2017/07/04 19:58:27]

sure

+    std::string error;
+  };
+
   void Sleep(int millis);
 
   class Mutex
   {
   public:
 #ifdef WIN32
     CRITICAL_SECTION nativeMutex;
 #else